Oxytocin receptor polymorphism influences characterization of harm avoidance by moderating susceptibility to affectionless control parenting

Abstract Introduction Oxytocin receptor (OXTR) gene polymorphism reportedly moderates effects of negative environments during childhood on mental function and behavior such as depressive symptoms and externalizing problems. This study examined OXTR gene polymorphism effects on personality traits in healthy participants, considering interaction effects of polymorphism with affectionless control (AC) parenting which is one of the dysfunctional and pathogenic parenting styles. Methods For 496 Japanese volunteers, personality was evaluated using the Temperament and Character Inventory. The Parental Bonding Instrument, which has subscales of care and protection, was used to assess perceived parental rearing. AC parenting was defined as low care and high protection. A/G polymorphism of the OXTR gene (rs53576) was detected using TaqMan SNP Genotyping Assay. Results Two‐way analysis of covariance revealed significant interaction effects between the genotype and the number of AC parents on scores of harm avoidance, with no significant main effect of genotype on any personality. Post‐hoc analysis revealed that the harm avoidance scores were increased in a stepwise manner with respect to the increase of the number of AC parents in the A allele carriers. No similar association was observed in the A allele noncarriers. Conclusion The results of this study suggest that OXTR polymorphism influences characterization of harm avoidance by moderating susceptibility to AC parenting.

Rs53576, an A/G single nucleotide polymorphism in the intron three of the OXTR gene, has been investigated extensively because of its association with human social behaviors (Cataldo et al., 2018). Two metaanalyses using genetic association studies show that the A allele is associated with lower sociality (Li et al., 2015) and empathy (Gong et al., 2017). A neuroimaging study of healthy human volunteers revealed that the A allele of this polymorphism is associated with decreased hypothalamus volume, increased amygdala volume, and increased connection between the amygdala and hypothalamus during perceptual processing for facial emotion (Tost et al., 2010). Reportedly, the hippocampal volume is smaller in A allele carriers with high emotional trauma than in those with minimal emotional trauma, but no such relation was observed in A allele noncarriers (Malhi et al., 2020).
In relation to personality, effects of rs53576 polymorphism on personality traits have been examined (Cornelis et al., 2012;Saphire-Bernstein et al., 2011;Tost et al., 2010;Wang et al., 2014) using the Tridimensional Personality Questionnaire (Cloninger et al., 1994), the Life Orientation Test (Scheier et al., 1994), and the Rosenberg Self-Esteem Scale (Rosenberg, 1965). However, these studies produced inconsistent results related to harm avoidance (Tost et al., 2010;Wang et al., 2014) and optimism (Cornelis et al., 2012;Saphire-Bernstein et al., 2011). Therefore, associations of this polymorphism with personality must be re-examined. Furthermore, the results of recent studies particularly addressing the gene-environment interactions suggest that A allele carriers of the polymorphism are sensitive to childhood negative environments, leading to increased depressive symptoms (Kazantseva et al., 2020;Thompson et al., 2014) and behavioral problems (Choi et al., 2019). Nevertheless, no report has described a study examining effects of interaction between this polymorphism and environments on personality traits. Therefore, this study examined OXTR polymorphism effects on personality traits, as evaluated using the Temperament and Character Inventory (TCI; Cloninger et al., 1994), considering interaction effects of this polymorphism with affectionless control (AC) parenting which is a combination of poor-care and over-protection and is one of the dysfunctional and pathogenic parenting styles (Martin & Waite, 1994;Parker, 1979;Parker, 1983), as assessed using the Parental Bonding Instrument (PBI) ).
Exclusion criteria were (1) participants with current or past history of psychiatric disorder according to the Diagnostic and Statistical Manual of Mental Disorders -IV (American Psychiatric Association, 1994) and (2) participants whose parents had divorced or died before the child was 16 years old. This study was performed in accordance with the Declaration of Helsinki. The Ethics Committee of the Yamagata University School of Medicine approved this study (approval no. 31/26.12.2002). Informed consent to this study was acquired in writing from all participants.

Assessment of personality and AC parenting
Personality traits of participants were evaluated using the Japanese version of the TCI, which has high validity and internal consistency (Cloninger et al., 1994;Kijima et al., 1996). The TCI has seven dimensions: harm avoidance, novelty seeking, reward dependence, persistence, self-directedness, cooperativeness, and self-transcendence.
Perceived parental rearing was assessed using the Japanese version of the PBI, which is verified to have high reliability and validity (Ogawa, 1981;Parker et al., 1979). The PBI has care and protection subscales from parents: paternal care, paternal protection, maternal care, and maternal protection. Each score was regarded as "low" if it was equal to or lower than the median, and "high" if it was higher than the median. AC parenting was inferred when participants had low care and high protection . Reportedly, AC parenting is a predisposing factor for neurotic depression in adulthood (Parker, 1979;Parker, 1983) and suicidality (Martin & Waite, 1994). Our earlier studies also demonstrate that AC parenting increases personality vulnerability to depression, such as interpersonal sensitivity (Otani et al., 2009) and dysfunctional attitude (Otani et al., 2014).

Genotyping
DNA was collected from peripheral blood using a QIAamp DNA Blood Kit (Qiagen, Tokyo, Japan). To detect the rs53576 of the OXTR gene, TaqMan SNP Genotyping Assay (C_3290335_20; Thermo Fisher Scientific) and TaqPath Master Mix (Thermo Fisher Scientific) were used. For this study, the OXTR genotypes were divided into two groups: A allele carriers (A/A + A/G) and A allele noncarriers (G/G), according to earlier meta-analyses showing that the A allele is dominantly related to sociality (Li et al., 2015) and empathy (Gong et al., 2017).

Statistical analyses
Statistical analyses were conducted using software (SPSS 26; SPSS Japan Inc.    Two-way ANCOVA showed significant interaction effects of the genotype and the number of AC parents on the scores of harm avoidance (p = .028), whereas significant main effects of the OXTR genotype were not found on any TCI scores (Table 3). Post-hoc analysis showed that, in A allele carriers, the scores of harm avoidance were lower for participants with no parent with AC than for participants with one parent with AC (p = .002) and for participants with two parents with AC (p = .000) ( Figure 1). No similar association was observed for A allele noncarriers ( Figure 1).

DISCUSSION
For this study, significant interaction effects between the OXTR polymorphism and the number of AC parents on the scores of harm avoidance were found, with no main effect of genotype on any TCI dimension. Furthermore, scores of harm avoidance became higher in a stepwise manner with respect to the increase of the number of AC parents for A allele carriers, although no similar association was found for A allele noncarriers. It is suggested that high scores of harm avoidance are described as doubtful, pessimistic, shy, and fatigable, and that high harm avoidance is related to depression and anxiety disorders (Cloninger et al., 1994 (Choi et al., 2019;Kazantseva et al., 2020;Thompson et al., 2014). This report is the first of a study that specifically examines interaction effects between OXTR polymorphism and the environment on personality.
Three plausible mechanisms might be related to the present results.  (Fujisawa et al., 2019) and low maternal care (Unternaehrer et al., 2015), reportedly induce high methylation in several regions of the OXTR gene, which is linked to decreased OXTR expression (Kusui et al., 2001;Mamrut et al., 2013). Furthermore, the induction of the OXTR gene methylation is shown to be more apparent in A allele carriers than in A allele noncarriers (Reiner et al., 2015;Ziegler et al., 2015). Consequently, epigenetic mechanisms might be involved in the findings of the present study.
Several limitations exist for this study. First, the number of participants was not large. As a result, the number of A allele noncarriers was considerably small. Second, this study is a cross-sectional study design, that is, the TCI and the PBI were assessed simultaneously, suggesting that the causative relation remains unclear. Third, the study participants were all Japanese. Therefore, these findings might be difficult to extend to other ethnic groups because of considerable ethnic diversity in allele frequencies of OXTR polymorphism (Kim et al., 2010).